Housing type pipe couplings are widely used for axially joining two pipes together in such a way as to create a non-leaking union between the pipe ends. To prevent leakage, it is often desirable to prevent longitudinal, angular or rotational movement of the pipe ends within the coupling. This type of coupling is called a rigid coupling
Generally, the coupling is formed of arcuate housing segments which are fastened around the pipe ends to form a generally ring-like coupling housing. Typically, two segments are used, a pair of arcuate or generally semicircular housing halves, which are fastened together, often bolted together. Housing halves are substantially U- or C-shaped in longitudinal (axial) cross section to provide room for gasket pieces. In some models, the inwardly projecting peripheral edges of the housing halves, also referred to as shoulders, are shaped with keys or lands for interlocking within circumferential grooves now commonly provided in the pipe ends.
The coupling is secured as bolts are tightened through bolt holes until the key segments engage the circumferential grooves on the pipe ends, thus fastening the pipes together. Where the two housing halves meet around the circumference of the pipes, a mating structure is often used to lock one housing half to the other and to add stability. A rubber gasket, also frequently U-shaped or C-shaped in longitudinal (axial) cross-section, is typically arranged within the coupling in a gasket pocket formed by the U-shaped longitudinal cross section of the coupling housing, such that when the housing halves are tightened against the pipe ends the inner peripheral edges of the gasket are sealed against the pipe end portions.
Pipe ends are typically grooved using either a rolled or cut groove. A roll groove uses a rolling machine to displace the pipe walls forming a curved-edged groove containing a top corner and a bottom corner with the top corner to corner separation longer than the bottom corner to corner separation. The gasket sealing surface is the distance between the outer groove wall and the end of the pipe. A cut groove removes pipe material to form a groove with straight walls perpendicular to the longitudinal axis of the pipe and therefore has no rounded corners.
Whether rolled or cut, the groove manufacturing method must accommodate significant tolerances set by the AWWA C-606 for gasket sealing surface, groove width, groove diameter, and outer diameter. Any pipe coupling must also accommodate such dimensional variations.
Several designs are in use which attempt to minimize longitudinal, angular or rotational movement of the pipe ends within the coupling. Angled self-adjusting couplings and tongue and groove style rigid couplings have slightly oval variable internal circumferential diameters that shrink when a coupling is tightened until it grips the pipe ends eliminating angular movement caused by variable outer diameters and groove depths. However, as key width is smaller than groove width to facilitate easy installation within tolerances, space between the key and corresponding groove allows for some longitudinal movement when pipes are exposed to pressure thrusts or thermal movement. Through these designs, longitudinal movement is effectively reduced, but never completely eliminated.
It is believed that conventional or known ‘pre-assembled’ coupling designs have not taken hold in the industry because they appear to require complex in situ assembly. For many years, in situ assembly and installation of such couplings has been the rule because no better alternative appeared to be practical, and manufacturers were offering single piece round gaskets that purportedly stretched to fit the pipe at hand, or else were using multi-part gasket pieces. For instance one known pre-assembled coupling, using a single piece gasket, has advertised that assembly would be simple and easy, even in hard to reach places, because the gasket would purportedly stretch to accommodate the inserted pipe until it could be locked in and sealed by tightening the coupling's bolts. However, market research suggests that this design has not acquired a large following, and laboratory tests have shown what is believed to be an unacceptable seal failure rate, due either to incomplete or inconsistent assembly efforts on site, or to actual tears or cuts in the gasket itself believed to have been caused by the very difficult pipe insertion conditions, often requiring wild gyrations of the pipe and or the gasket to get them to come together at all.
Other conventional couplings are multi-part disassembled pipe coupling components that must be assembled on site, and in situ, typically overhead and in hard to reach places. These couplings use some kind of separate member either inside the upper and lower housing halves, or intermediate to the upper and lower housing halves, and typically integral with some kind of sealing material, in a reported attempt to apply some kind of four-way pressure to the pipe sealing material. Typically these separate members are fitted in grooves or channels provided in upper and lower arcuate housing halves. None of these previously disclosed couplings appear to be in current use, and there is reason to believe that none of them was ever effective at rigidly joining and sealing two pipe segments together. It is also believed that none of them actually deliver real four-way compression either very well, or very consistently.
None of these couplings use a one-piece sealing gasket, and none of them can be installed onto respective pipe ends without first being disassembled. Also none of the couplings have slidably engaging dihedral angular faces where bridge segments engage corresponding upper and lower housing segment faces, such that all four segments move towards the center of the coupling as the bolts and nuts are tightened.
Housing type mechanical couplings on grooved-end pipes usually have two housing segments, some kind of rubber gasket and two pairs of bolts and nuts as shown in FIG. 1. When a coupling is installed on a pipe, it must be done in components, or a preassembled coupling unit must be broken down into those components. Then, if the sealing gasket is conventional one-piece gasket having an inner diameter smaller than the pipe it is designed to fit (see FIG. 2), it must be stretched and mounted it onto the pipe ends. Finally the two housing halves are placed on the gasket, bolts and nuts inserted, and the nuts fastened tight.
When a large number of such couplings are to be installed, higher work efficiency is required to shorten work time and to reduce installation costs. So assembly on site and gasket stretching, both time consuming and sometimes very difficult depending on conditions and location of joint, are inefficient and can become quite expensive.
What is needed, in order to raise efficiency of installation work, is a new type coupling to solve those technical problems, while at the same time still effectively eliminating longitudinal, angular and rotational movement of the pipe ends within the coupling housing.